A saline-alkali soil phosphorus activation slow-release granule and a preparation method and application thereof

Abstract

A saline-alkali soil phosphorus activation slow-release granule, a preparation method and application thereof, a multi-layer spherical coating structure composed of a core material, an inner coating, a wall material and an outer coating from inside to outside; wherein the core material is composed of modified diatomite, fulvic acid, maltose, ammonium sulfate and mixed bacterial agent; the inner coating is composed of mixed starch, polyvinyl alcohol and plasticizer; the wall material is composed of citric acid and oxalic acid; and the outer coating is composed of vegetable oil and resin. The granule is a "double-coated film" type saline-alkali soil phosphorus activation granule which takes into account the functions of chemical alkali reduction and phosphorus dissolution and microbial phosphorus dissolution and activation, promotes the transformation of closed and accumulated phosphorus into available state, and has long-acting slow-release effect, breaks through the existing bottlenecks of poor applicability, short action time, mismatch between phosphorus activation release and crop phosphorus demand, etc. of the existing phosphorus activator in saline-alkali soil, and is suitable for phosphorus activation and synergistic utilization of different degrees and types of saline-alkali soil in northern China.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of agriculture and ecology, and particularly relates to a saline-alkali soil phosphorus activation slow-release granule, a preparation method and application thereof. BACKGROUND

[0002] Phosphorus is one of the three essential nutrients for crop growth. Phosphorus is not only a structural component of various macromolecular compounds in plants, but also actively participates in various metabolic processes such as carbohydrate metabolism and nitrogen metabolism in plants, and is one of the important nutrient limiting factors for crop growth and high yield. The phosphorus required for crop growth mainly comes from soil, and the occurrence form of phosphorus in soil directly affects the availability of phosphorus in soil phosphorus pool and the absorption and utilization of phosphorus by crops.

[0003] Soil salinization seriously restricts the utilization efficiency of soil phosphorus nutrients. Studies have shown that the availability of phosphorus in saline-alkali soil and the absorption and utilization rate of crops are low, and the adsorption capacity of phosphorus in saline-alkali soil is about 3 times that in non-saline-alkali soil. First, the high salt content in soil deteriorates the soil physical and chemical properties, reduces the activity of soil microorganisms, affects the soil phosphorus transformation process, and reduces the biological and chemical availability of soil phosphorus; second, the phosphorus applied to saline-alkali soil is easily precipitated with potassium, calcium and magnesium to form insoluble K-P, Ca-P and Mg-P oxides, thereby reducing the availability of phosphorus; third, the high Na + in saline-alkali soil exists in the form of soluble sodium phosphate salt, and crops absorb too much Na + , which is toxic to plant growth and development and phosphorus absorption; finally, the high pH of saline-alkali soil causes water-soluble phosphate to react with free calcium ions to form phosphorus calcium with extremely low availability.

[0004] Therefore, in view of the beneficial transformation and efficient utilization of saline-alkali soil phosphorus pool, it is of great significance to construct a slow-release saline-alkali soil phosphorus activator based on low-molecular-weight organic acid rapid activation, phosphorus-dissolving and phosphorus-degrading microorganism long-term activation, which can improve the nutrient utilization rate of saline-alkali soil, fertilize and increase the capacity of the soil, reduce the application of fertilizers and increase the efficiency, and prevent and control non-point source pollution. Compared with the prior art, the method has the advantages of being suitable for saline-alkali stress environment, having rapid and long-term effects, and being mild and slow-release.

[0005] Chinese Invention CN109777438A discloses a preparation for activating phosphorus in soil, a preparation method, an application method and application thereof. Through the synergistic promotion effect of Trichoderma fungi and inorganic nano materials, the secretion of phosphorus-dissolving enzymes such as phytase and phosphatase in soil can be effectively promoted, and the original insoluble phosphorus in soil can be released as available phosphorus.

[0006] Chinese invention CN105542789A discloses a kind of alkaline soil phosphorus activator, contains rich organic matter and nitrogen phosphorus potassium and other nutrient elements, and contains rich phosphorus-solubilizing bacteria, by limiting the use ratio of furfural residue, potassium sulfate, wood vinegar and phosphorus-solubilizing bacteria agent, the application of this phosphorus activator on alkaline soil can improve the soil phosphorus supply capacity and phosphorus fertilizer utilization efficiency.

[0007] Chinese invention CN111961608A discloses a kind of phosphorus-dissolving bacteria, phosphorus-dissolving bacteria agent, biological bacteria fertilizer and application, which can increase the content of soil neutral phosphatase, water-soluble phosphorus and sodium bicarbonate inorganic phosphorus, reduce the content of residual phosphorus in soil, and promote the transformation of active state and low active state phosphorus in soil to active state phosphorus.

[0008] Chinese invention CN101003737A discloses a kind of soil phosphorus activator, by limiting the proportion of aspergillus niger phosphorus-dissolving bacteria agent, peat, corn axis powder, vinasse, allantoin and nitro ammonium, the soil phosphorus supply capacity for crops is improved, the production cost is reduced, and the crop yield is improved.

[0009] From the above existing technology, the current soil phosphorus activation method mainly aims at non-saline-alkali land, and promotes the transformation of difficult-to-dissolve phosphorus to soluble phosphorus by applying organic or inorganic acid materials or high-efficiency phosphorus-dissolving and phosphorus-solubilizing microorganisms. However, the unique physicochemical and biological properties of saline-alkali land often have unusual nutrient transformation and migration processes. The existing phosphorus activation method has weak applicability, poor effect and short effective period in saline-alkali land, and the root cause lies in the inhibition of microbial activity and plant absorption by saline-alkali stress, which promotes the transformation of phosphorus to combined state. Therefore, it is urgent to consider the special physicochemical and biological properties of saline-alkali land, construct a kind of slow-release phosphorus activator that is suitable for soil saline-alkali stress, has organic-inorganic and microbial activation composite functions, and comprehensively considers long-term and quick-acting properties, and establish a matching application method for different types and degrees of saline-alkali land. SUMMARY

[0010] The technical problem solved by the present application is that the present application comprehensively considers the problems of weak phosphorus availability in saline-alkali land, easy fixation and passivation of exogenous phosphorus, and low absorption and utilization efficiency of crops, and proposes a kind of saline-alkali land phosphorus activation slow-release granules and its preparation method and application. The granules have the functions of chemical alkali reduction and phosphorus dissolution and microbial phosphorus dissolution and phosphorus activation, promote the transformation of closed and stored phosphorus to available state, and are long-acting and slow-releasing "double-coated" saline-alkali land phosphorus activation granules. The present application breaks through the bottlenecks of poor applicability, short action period, and mismatch between phosphorus activation release and crop phosphorus demand of existing phosphorus activators, and is suitable for soil phosphorus activation and synergistic utilization of different degrees and types of saline-alkali land in northern China.

[0011] The technical scheme is a saline-alkali soil phosphorus activation slow-release granule, which comprises a multi-layer spherical coating structure of core material, inner coating, wall material and outer coating from inside to outside; the core material is composed of modified diatomite, fulvic acid, maltose, ammonium sulfate and mixed bacterial agent; the inner coating is composed of mixed starch, polyvinyl alcohol (PVA) and plasticizer; the wall material is composed of citric acid and oxalic acid; the outer coating is composed of vegetable oil and resin; the mass ratio of the components of the core material is as follows: modified diatomite 20-40 parts, fulvic acid 3-6 parts, maltose 2-5 parts, ammonium sulfate 1-2 parts and mixed bacterial agent 1-2 parts; the mass ratio of the components of the inner coating is as follows: mixed starch 2-4 parts, polyvinyl alcohol 1.5-3 parts and plasticizer 1-2 parts; the mass ratio of the components of the wall material is as follows: citric acid 30-50 parts and oxalic acid 40-60 parts; and the mass ratio of the components of the outer coating is as follows: vegetable oil 3-6 parts and resin 1-2 parts.

[0012] The above modified diatomite is natural diatomite with SiO2 content ≥70wt.%, particle size 0.05-0.1mm, which is calcined at 400-450℃ for 1-2h or modified in 1.5-2mol / L sulfuric acid at temperature 35-40℃ for 35-45min, and the specific surface area of the modified diatomite is ≥100m 3The said saline-alkali soil phosphorus activation slow-release granules, wherein the modified diatomite is 20 parts, the said fulvic acid is 5 parts, the said maltose is 3 parts, the said ammonium sulfate is 1 part, the said mixed bacterial agent is 1 part, the said mixed bacterial agent is a mixture of Bacillus megaterium, Aspergillus niger and Penicillium oxalicum in a weight ratio of 1:1:1, and the said mixed bacterial agent is a powder with a particle size of 100 mesh; 13.1% of water is further added and stirred to form granules with a diameter of 0.3-0.7 mm; the said mixed starch is 3 parts, the said polyvinyl alcohol is 2 parts, and distilled water is added in a weight ratio of 1:5, and then the mixture is placed in a water bath at 90°C and stirred for 40 min; 1.5 parts of glycerol is further added and stirred for 40 min, and then the mixture is cooled to room temperature to prepare an inner coating material; the inner coating material is uniformly coated on the surface of the above granules; the said citric acid is 40 parts, the said oxalic acid is 50 parts, and the said coated granules are further drum granulated to form granules with a diameter of 0.5-1.0 mm.

[0013] The saline-alkali soil phosphorus activation slow-release granules described above, wherein the modified diatomite is 20 parts, the said fulvic acid is 5 parts, the said maltose is 3 parts, the said ammonium sulfate is 1 part, the said mixed bacterial agent is 1 part, the said mixed bacterial agent is a mixture of Bacillus megaterium, Aspergillus niger and Penicillium oxalicum in a weight ratio of 1:1:1, and the said mixed bacterial agent is a powder with a particle size of 100 mesh; 13.1% of water is further added and stirred to form granules with a diameter of 0.3-0.7 mm; the said mixed starch is 3 parts, the said polyvinyl alcohol is 2 parts, and distilled water is added in a weight ratio of 1:5, and then the mixture is placed in a water bath at 90°C and stirred for 40 min; 1.5 parts of glycerol is further added and stirred for 40 min, and then the mixture is cooled to room temperature to prepare an inner coating material; the inner coating material is uniformly coated on the surface of the above granules; the said citric acid is 40 parts, the said oxalic acid is 50 parts, and the said coated granules are further drum granulated to form granules with a diameter of 0.5-1.0 mm.

[0014] The preparation method of the saline-alkali soil phosphorus activation slow-release granules is as follows: Step 1: modified diatomite, fulvic acid, maltose, ammonium sulfate and mixed bacterial agent are mixed according to the mass fraction, 10-15 wt.% of water based on the total weight is added, and the mixture is fully stirred and uniformly mixed, and granulated into core material particles with a diameter of 0.5-1 mm; Step 2: mixed starch and polyvinyl alcohol are mixed according to the mass fraction, distilled water is added according to a weight ratio of 1:(4-5), and then placed in a 90℃ water bath, stirred for 35-40 min, then glycerol is added and stirred for 40-45 min, and then cooled to room temperature to prepare an inner coating material; Step 3: the inner coating material is uniformly coated on the core material particles, and the thickness of the inner coating is 0.05-0.1 mm; Step 4: citric acid and oxalic acid are mixed according to the mass fraction, and the coated core material prepared in Step 2 is added, and then drum granulation is performed to obtain particles with a diameter of 0.6-1.1 mm; Step 5: plant oil is added to a reaction tank and fully stirred and mixed, the corresponding mass fraction of resin is added, nitrogen gas is injected into the reaction tank for 10 min and air is discharged, the reaction tank is heated, the temperature is raised for 5 hours, the reaction temperature is set to 120-150℃, and the temperature is kept for 5 hours and then reduced to 40-80℃ to prepare an outer coating material; Step 6: the outer coating material is sprayed on the surface of the particles by using a spray condensation granulation, and the condensation spray conditions are that the outer coating material feeding temperature is 60-80℃, the condensation temperature is 0-5℃, and the thickness of the outer coating is 0.02-0.04 mm.

[0015] The slow-release granules are applied in the activation of saline-alkali soil phosphorus.

[0016] The application specific method is as follows: the application amount and frequency are different for different degrees of soil salinity, for mild saline-alkali soil with a total salt content of <3 g / kg or 7.5<pH<8.5, the strip application amount is 10-20 kg per mu, the hole application amount is 10-15 kg per mu, and the application frequency is once every 4-5 years; for moderate saline-alkali soil with a total salt content of 3-6 g / kg or a pH value of 8.5-9.5, the strip application amount is 20-40 kg per mu, the hole application amount is 15-30 kg per mu, and the application frequency is once every 3-4 years; for severe saline-alkali soil with a total salt content of >6 g / kg or a pH of >9.5, the strip application amount is 40-60 kg per mu, the hole application amount is 30-40 kg per mu, and the application frequency is once every 2-3 years.

[0017] Beneficial effects: (1) rapid activation of phosphorus. The low-molecular-weight organic acids (such as citric acid and oxalic acid in the wall material) rapidly reduce the pH and residual sodium carbonate of the saline-alkali soil, promote the dissolution of calcium phosphate compounds such as hydroxyapatite, dicalcium phosphate, and octacalcium phosphate, and release phosphorus, which can increase the supply capacity of soil available phosphorus by 1-14 times within 24 hours (the higher the concentration of organic acid, the greater the amount of phosphorus released).

[0018] (2) Long-acting and persistent activation. Considering the activation characteristics of different types of organic acids, different effective periods of organic acids are combined (the effective period of citric acid is 2-3 times that of oxalic acid), the release of phosphorus and the phosphorus demand characteristics of crops during the seedling and vigorous growth stages are matched, and the activation and release of phosphorus are more accurately targeted, increasing the effective period from 15 days to 50 days.

[0019] (3) Improve biological activity. Through high-efficiency phosphorus-solubilizing microorganisms such as Bacillus megaterium and Aspergillus niger (modified diatomite in the core material provides a carrier for microorganisms, fulvic acid and maltose provide carbon sources for microbial activity, and ammonium sulfate provides nitrogen sources for microbial activity and adjusts the carbon-nitrogen ratio), a chemical and microbial synergistic "relay" activated phosphorus is formed, further promoting the mineralization, activation, and absorption of organic phosphorus in the soil.

[0020] (4) Time and batch release. By taking advantage of the differences in hydrophilicity and swelling between the inner coating (mixed starch, polyvinyl alcohol, and plasticizer) and the outer coating (plant oil and resin), the outer coating is more easily water-soluble and swells, the wall material releases organic acid to quickly dissolve and combine with phosphorus, and the inner coating material has a long effective period, releasing the microorganism phosphorus-solubilizing bacteria in the core material after the organic acid is consumed, further activating and releasing the poorly soluble phosphorus, and making the phosphorus release in time and batches, improving the phosphorus utilization rate by 3-5 percentage points.

[0021] (5) Multiple synergistic effects. In addition to the functions of acid-base neutralization, activation of phosphorus, and improvement of available phosphorus supply, it also has the functions of loosening soil and promoting soil aggregation, and through multiple effects such as physical reduction, chemical solubilization, and biological activation, the activated phosphorus is synergistically enhanced: the porous modified diatomite can improve the soil physical structure and water and air permeability, and accelerate the leaching of soil salinity; low-molecular-weight organic acids can quickly reduce the soil microenvironment pH and enhance the activation and release of poorly soluble phosphorus; fulvic acid, ammonium sulfate, and microbial agents can promote the proliferation of beneficial microorganisms in the soil, improve the stress tolerance of crops, and promote the formation of soil aggregates through the action of extracellular enzymes, etc., having the comprehensive effects of acid reduction, activated phosphorus, and soil improvement. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Structure diagram of slow-release granules;

[0023] Figure 2 Soil phosphorus desorption amount after activation of different types and concentrations of organic acids for 2 hours;

[0024] Figure 3 Soil phosphorus desorption amount at different time periods under the treatment of different organic acids (2 mmol / L);

[0025] Figure 4 Soil pH, salt content, and available phosphorus content during the growth period of corn under the treatment of different activation agents (a: pH; b: salt content; c: available phosphorus); Detailed Implementation

[0026] The following specific embodiments are further illustrations of the present invention, but do not imply that the scope of the invention is limited to the examples given. This invention breaks through the traditional application method of "single, large-scale application per season" of phosphate fertilizer in saline-alkali land, creating a "double-coated" type phosphorus activation slow-release granular agent: the outer layer is a low-molecular-weight organic acid with high solubility, high activity, and different shelf lives, which rapidly and continuously lowers the pH, promoting the dissolution of calcium phosphate compounds and the release of phosphorus; the inner layer is a salt-alkali resistant microbial agent with high phosphorus-solubilizing ability, using modified diatomaceous earth as a colonization carrier to enhance microbial activity and organophosphate activation efficiency; utilizing the differences in solubility and swelling capacity between the outer and inner coating materials, time-sharing and batch-wise release is achieved. Through the above combined effect, the shortcomings of traditional phosphorus activation methods, such as short shelf life, low efficiency, and poor compatibility with crop growth, are overcome.

[0027] Example 1:

[0028] This is a moderately to slightly saline-alkali land in the Ningxia irrigation area. Located in Team 3, Baofeng Village, Baofeng Town, Pingluo County, Ningxia, the soil type is gray-calcareous soil with a silty clay texture. The average soil salinity in the topsoil (0-20cm) is 2.59g / kg, pH is 8.73, average organic matter content is 14.93g / kg, total nitrogen is 0.49g / kg, total phosphorus is 748.4mg / kg, and available phosphorus is 22.5mg / kg. The previous crop was dual-purpose grain and forage silage corn. Soil samples were collected, air-dried, ground, and sieved before being used for cultivation experiments (March 23, 2022 – June 18, 2022). The main implementation steps are as follows:

[0029] (1) Backfilling. The above soil samples were prepared according to a ratio of 1.4 g / cm³. 3 The density was measured and filled into plastic measuring cups, with 70g of soil in each cup, for a total of 108 measuring cups.

[0030] (2) Preparation of organic acids. Four low molecular weight organic acids, namely citric acid, oxalic acid, malic acid and acetic acid, were selected and dissolved in distilled water to prepare eight concentrations of 0.05, 0.10, 0.50, 1.0, 2.0, 5.0, 10.0 and 20.0 mmol / L. Distilled water (0), 0.05, 0.10, 0.50, 1.0, 2.0, 5.0, 10.0 and 20.0 mmol / L organic acid were added to 108 measuring cups, for a total of 36 treatments. Each treatment was repeated 3 times (4 organic acids, 9 concentration gradients for each organic acid).

[0031] (3) Constant temperature incubation. Add 12.6 mL (close to field capacity) to each measuring cup, seal the measuring cup with plastic wrap, and place it in a constant temperature incubator at 25℃ for incubation;

[0032] (4) Soil sample collection. After 2, 5, 10, 15, 20, 24, 37, 50 hours of constant steady culture, the soil samples were taken out and the content of soil available phosphorus was determined, and the amount of soil phosphorus desorption under different organic acid concentrations and time was calculated (soil phosphorus desorption amount = the content of available phosphorus in each organic acid culture soil sample - the content of available phosphorus in distilled water culture soil sample).

[0033] Figure 2 The effect of 2 hours of activation by different concentrations of citric acid, oxalic acid, malic acid and acetic acid on the release of phosphorus is shown. It can be seen that the type and concentration of organic acid have a great influence on the release of soil phosphorus. When the concentration of organic acid is 0-1 mmol / L, the activation effect of organic acid on soil phosphorus is not great, and the difference is not great. With the increase of the concentration of organic acid (1-20 mmol / L), the activation amount of organic acid on soil phosphorus gradually increases, basically following the order: citric acid > oxalic acid > malic acid > acetic acid; when the concentration of organic acid is 1-20 mmol / L, the concentration and the amount of soil phosphorus release are basically in an exponential growth relationship, indicating that increasing the concentration of citric acid and oxalic acid (5-20 mmol / L) can significantly promote the release of soil phosphorus. Overall, the difference in the activation of low-concentration organic acid (<2 mmol / L) on saline-alkali soil phosphorus is small, and when the concentration of organic acid is more than 5 mmol / L, the excitation effect of citric acid and oxalic acid on the release of saline-alkali soil phosphorus is significantly stronger than that of malic acid and acetic acid.

[0034] Figure 3 The soil phosphorus desorption amount under different time periods under the treatment of each organic acid at 2 mmol / L of organic acid is shown. It can be seen that with the extension of the action time of organic acid and soil, the release of soil phosphorus shows a dynamic change. Overall, the release of phosphorus is completed in a short time and reaches equilibrium. Within 2-5 h, for citric acid, oxalic acid and malic acid, the content of dissolved phosphorus decreases by 30.3%, 7.4 and 16.3% respectively; after 5 h, the change amplitude of phosphorus release is very small; at the same time, for acetic acid, the activation of phosphorus has a small decrease. In a short time, the soil phosphorus activated by organic acid may be the surface unstable state of phosphorus; with the extension of the reaction time, the dissolution of phosphate crystal compounds dominates. In addition, Ca 2+ and Mg 2+ in the soil recombine with PO4 3- to form insoluble Ca-P and Mg-P precipitates, which can also cause the decrease of phosphorus and cause the fluctuation of phosphorus desorption amount. Overall, the excitation effect of citric acid and oxalic acid on the release of saline-alkali soil phosphorus is significantly stronger than that of malic acid and acetic acid. In summary, the activation effect of citric acid and oxalic acid on the soil phosphorus of saline-alkali soil is significantly better than that of malic acid and acetic acid, whether in efficiency or duration.

[0035] Example 2:

[0036] The experiment was conducted in the middle and light saline-alkali land of irrigation area in Ningxia. The soil type was gray calcareous soil, and the texture was silty clay. The average soil salinity in the 0-20 cm soil layer was 2.59 g / kg, the pH was 8.73, the average organic matter content was 14.93 g / kg, the total nitrogen content was 0.49 g / kg, the total phosphorus content was 748.4 mg / kg, the available phosphorus content was 22.5 mg / kg, and the previous crop was forage and grain storage maize. After the soil samples were collected, they were dried, ground, and sieved in the laboratory. The maize variety SN211 was planted in pots from June 5 to September 26, 2022. The main implementation steps are as follows:

[0037] (1) Preparation of phosphorus activator: seven kinds of phosphorus activators were prepared as follows:

[0038] Activator A: Mix 40 parts of citric acid and 50 parts of oxalic acid, add 12.5% water based on the total weight, mix thoroughly, and granulate into 0.5-1.0 mm diameter particles.

[0039] Activator B: Mix 20 parts of modified diatomite, 5 parts of fulvic acid, 3 parts of maltose, 1 part of ammonium sulfate, and 1 part of mixed bacteria (Bacillus megaterium, Aspergillus niger, and Penicillium oxalicum in a weight ratio of 1:1:1), add 12.5% water based on the total weight, mix thoroughly, and granulate into 0.5-1.0 mm diameter particles.

[0040] Activator C: Mix 5 parts of fulvic acid, 3 parts of maltose, 1 part of ammonium sulfate, and 1 part of mixed bacteria (same as above), add 12.5% water based on the total weight, mix thoroughly, and granulate into 0.5-1.0 mm diameter particles.

[0041] Activator D: Mix 20 parts of modified diatomite and 1 part of mixed bacteria (same as above), add 12.5% water based on the total weight, mix thoroughly, and granulate into 0.5-1.0 mm diameter particles.

[0042] Activator E: modified diatomite 20 parts, fulvic acid 5 parts, maltose 3 parts, ammonium sulfate 1 part, mixed bacterial agent (Bacillus megaterium, Aspergillus niger, Penicillium oxalicum mixed in a weight ratio of 1:1:1) 1 part are mixed uniformly, water accounting for 12.5% of the total weight is added and stirred thoroughly, granulated into particles with a diameter of 0.3-0.7 mm; mixed starch 3 parts, polyvinyl alcohol 2 parts are mixed, distilled water is added in a weight ratio of 1:5, then placed in a 90°C water bath, stirred for 40 min, glycerol 1.5 parts is added and stirred for another 40 min, then cooled to room temperature to prepare an inner coating material, which is uniformly coated on the surface of the above particles; citric acid 40 parts, oxalic acid 50 parts are mixed with the coated particles, further drum granulated into particles with a diameter of 0.5-1.0 mm;

[0043] Activator F: fulvic acid 5 parts, maltose 3 parts, ammonium sulfate 1 part, mixed bacterial agent (same as above) 1 part are mixed uniformly, water accounting for 12.5% of the total weight is added and stirred thoroughly, granulated into particles with a diameter of 0.3-0.7 mm; mixed starch 3 parts, polyvinyl alcohol 2 parts are mixed, distilled water is added in a weight ratio of 1:5, then placed in a 90°C water bath, stirred for 40 min, glycerol 1.5 parts is added and stirred for another 40 min, then cooled to room temperature to prepare an inner coating material, which is uniformly coated on the surface of the above particles; citric acid 40 parts, oxalic acid 50 parts are mixed with the coated particles, further drum granulated into particles with a diameter of 0.5-1.0 mm.

[0044] Activator G: modified diatomite 20 parts, mixed bacterial agent (same as above) 1 part are mixed uniformly, water accounting for 12.5% of the total weight is added and stirred thoroughly, granulated into particles with a diameter of 0.3-0.7 mm; mixed starch 3 parts, polyvinyl alcohol 2 parts are mixed, distilled water is added in a weight ratio of 1:5, then placed in a 90°C water bath, stirred for 40 min, glycerol 1.5 parts is added and stirred for another 40 min, then cooled to room temperature to prepare an inner coating material, which is uniformly coated on the surface of the above particles; citric acid 40 parts, oxalic acid 50 parts are mixed with the coated particles, further drum granulated into particles with a diameter of 0.5-1.0 mm.

[0045] (2) The steps of the pot experiment are as follows:

[0046] Test treatment: 8 treatments were set, respectively CK (conventional fertilization), PA-A (conventional fertilization + phosphorus activator A), PA-B (conventional fertilization + phosphorus activator B), PA-C (conventional fertilization + phosphorus activator C), PA-D (conventional fertilization + phosphorus activator D), PA-E (conventional fertilization + phosphorus activator E), PA-F (conventional fertilization + phosphorus activator F), PA-G (conventional fertilization + phosphorus activator G). Each treatment was repeated 3 times, a total of 24 plastic buckets, each plastic bucket (diameter 25 cm, height 26 cm) filled with soil 13.7 kg (soil height 20 cm). The bottom of the plastic bucket was provided with a drainage hole, and if there was salt leaching during irrigation, it was collected in the tray and then poured back into the soil to ensure that there was no salt leaching.

[0047] Base fertilizer application: all treatments were uniformly fertilized, and the nitrogen fertilizer in the base fertilizer was urea (N: 46.4%), and the phosphorus fertilizer was superphosphate (P2O5: 14%). The N application amount was 20 kg / acre (3.2 g of urea per bucket), and the P2O5 application amount was 8 kg / acre (4.2 g of superphosphate per bucket); among them, urea was applied according to the base and the ratio of 4:3:3, that is, 40% of urea was applied as base fertilizer, 30% of urea was applied at the jointing stage, and 30% of urea was applied at the flowering stage, and superphosphate was applied as base fertilizer at one time; The urea, superphosphate and 0-10 cm soil in the above base fertilizer amount were mixed uniformly and filled into the pot.

[0048] Activator application: the application amount was 25 kg / acre, and the strip application method was used, that is, 1.85 g of activator was applied in each plastic bucket, which was applied along the middle line of the plastic bucket 3 cm deep Small ditch, and the activator was applied and covered with soil.

[0049] Corn seeding and field management: corn was sown 2-3 cm away from the application strip of the activator, 3 corn seeds were sown in each bucket, and one plant was reserved after germination; The soil moisture content during the growth period of corn was monitored by weighing method, and water was added regularly to keep the soil moisture content at 60%-90% of the field water holding capacity.

[0050] Soil sampling: 0-10 cm soil samples near corn roots were collected at the seedling stage, jointing stage and maturity stage, and the soil salt, pH and available phosphorus content were determined, and the inorganic phosphorus component content at the maturity stage was also determined.

[0051] The change of soil pH of corn at different growth stages is as follows Figure 4a. It can be seen that for CK treatment without applying any activator, the soil pH is 8.75-8.91, PA-A significantly reduces the soil pH during the corn growth period, the soil pH is 8.37-8.66, PA-B, PA-C and PA-D have little effect on the soil pH during the whole corn growth period, between 8.64-8.79, lower than CK but higher than PA-A treatment; PA-E, PA-F and PA-G have the most significant effect on reducing the soil pH, the average soil pH during the corn growth period is 8.44, 8.48 and 8.47 respectively; compared with CK, the order of the effect on reducing the soil pH is PA-E>PA-G>PA-F>PA-A>PA-B>PA-D>PA-C. Overall, the effect of PA-E activator on reducing the soil pH is the most significant, followed by PA-G and PA-F. From Figure 4 b. It can be seen from the changes of soil salt content at different growth stages of corn that there is little difference in soil salt content among the activator treatments, the average value during the growth period is 2.35-2.56 g / kg. Overall, the application of activators does not cause significant increase in soil salt content. From Figure 4 c. From the soil available phosphorus content at different growth stages of corn, it can be seen that PA-A treatment is significantly higher than CK, PA-B, PA-C and PA-D treatments, and PA-E, PA-F and PA-G treatments are 18.9%, 11.2% and 10.3% higher than PA-A treatment respectively. Overall, the effect of PA-E on reducing soil pH and activating phosphorus is better than PA-F and PA-G, and significantly better than PA-A treatment, which indicates that single microorganism has certain effect on phosphorus activation in the later period, but is not as fast as organic acid, and the phosphorus activator with dual effect of low molecular organic acid and microorganism is significantly better than single low molecular organic acid activation effect, and the effect is more long-acting and persistent in the later period of corn growth.

[0052] Table 1 shows the soil inorganic phosphorus component content at different treatments at the corn harvest stage. It can be seen that the soil endogenous Ca 10 -P and Fe-P show significant difference (p<0.05) under different activator treatments, the soil Ca 10 -P and O-P content of PA-D treatment is the highest, 426.15 mg / kg and 44.46 mg / kg respectively, and the soil Ca 10 -P and O-P content of PA-E treatment is the lowest, 281.67 mg / kg and 22.47 mg / kg respectively, and the Fe-P and Al-P content is relatively high; comparing the soil endogenous phosphorus fertilizer and exogenous added phosphorus fertilizer, the Ca 10 -P, Ca8-P, Ca2-P and O-P content significantly decreases after applying PA-E activator, and Fe-P and Al-P significantly increases; with the continuous increase of the activator action time, the soil endogenous Ca 10-P, Ca2-P, and Al-P may be partially converted into organic phosphorus; exogenous organic phosphorus in the soil and Ca2-P, Ca8-P, Al-P, and Fe-P are partially converted into insoluble Ca... 10 -P and OP.

[0053] Table 1. Inorganic phosphorus content in soil under different treatments at maize harvest time.

[0054]

[0055] Example 3:

[0056] The Ningxia irrigation district has moderately to severely saline-alkali land. Located in Jiaoji Village and Liuzhong Village, Qukou Township, Pingluo County, Ningxia, the soil type is saline alluvial soil with a medium loam texture. Influenced by a small amount of clay, the moderately to severely saline-alkali land is distributed in an interspersed pattern. Selected moderately to severely saline-alkali plots showed an average soil salinity of 3.85–7.46 g / kg in the topsoil layer (0–20 cm), a pH of 8.41–8.82, an average organic matter content of 9.81 g / kg, total nitrogen of 0.33 g / kg, total phosphorus of 586.4 mg / kg, and available phosphorus of 17.9 mg / kg. The previous crop was abandoned land. Plot experiments were conducted on moderately (average topsoil salinity 4.12 g / kg) and severely (average topsoil salinity 6.48 g / kg) salinized plots, with a plot area of ​​80 m². 2 (8m×10m) Four phosphorus activator dosage gradients of 0, 10, 30, and 50 kg / mu were set up, for a total of 8 treatments, each of which was replicated three times. The details of each treatment are as follows:

[0057] Moderately saline-alkali land: MS0 (control, without phosphorus activator), MS 10 (Phosphorus activator 10kg / mu), MS 30 (Phosphorus activator 30 kg / mu) and MS 50 (Phosphorus activator 50 kg / mu)

[0058] Severely saline-alkali land: HSO (control, without phosphorus activator), HS 10 (Phosphorus activator 10kg / mu), HS 30 (Phosphorus activator 30kg / mu) and HS 50 (Phosphorus activator 50 kg / mu)

[0059] The specific implementation steps are as follows:

[0060] The activator is prepared as follows: 20 parts of modified diatomite, 5 parts of fulvic acid, 3 parts of maltose, 1 part of ammonium sulfate, and 1 part of mixed bacteria (Bacillus megaterium, Aspergillus niger, and Penicillium oxalicum mixed at a weight ratio of 1:1:1) are uniformly mixed, 13.1% of the total weight of water is added, and the mixture is fully stirred and mixed, and then granulated into particles with a diameter of 0.3-0.7 mm; 3 parts of mixed starch and 2 parts of polyvinyl alcohol are mixed, 5 parts of distilled water is added according to a weight ratio of 1:5, and then placed in a 90°C water bath for stirring for 40 min, 1.5 parts of glycerol is added and stirring is continued for 40 min, and then cooled to room temperature to prepare an inner coating material, which is uniformly coated on the surface of the above particles; 40 parts of citric acid and 50 parts of oxalic acid are mixed with the coated particles, and further drum granulation is performed to form particles with a diameter of 0.5-1.0 mm.

[0061] Land consolidation and base fertilizer application: The moderate and severe saline-alkali land plots are consolidated, and rotary tillage is used to ensure that the topsoil layer is mixed evenly; all treatments are uniformly fertilized, and the nitrogen fertilizer in the base fertilizer is urea (N: 46.4%), and the phosphorus fertilizer is superphosphate (P2O5: 14%). The N application amount is 20 kg / acre, and the P2O5 application amount is 8 kg / acre; among them, the urea is applied according to the base and subsequent ratio of 4:3:3, that is, 40% of the urea is applied as base fertilizer, 30% of the urea is applied at the jointing stage, and 30% of the urea is applied at the flowering stage, and the superphosphate is applied as base fertilizer at one time; the above base fertilizer amount of urea, superphosphate, and cultivated soil are rotary tilled and mixed evenly.

[0062] Activator application: The phosphorus activator is applied in a strip manner, that is, a ditch is opened along the corn planting row at a distance of 3-5 cm, the activator is applied in strips, and the soil is covered with a thickness of 2-3 cm; the planted crop is corn (Ningdan No. 11), and the drip irrigation under the film planting method is used, and the drip irrigation pipe is laid near the corn planting row; other planting management methods are consistent with the local ones.

[0063] Soil sampling: 0-15 cm soil samples are collected at the seedling stage, the large trumpet stage, and the mature stage, and the soil pH, salt content, and available phosphorus are measured, the corn grain yield is measured after harvesting, and the phosphorus content is measured, and the phosphorus agronomic utilization rate is calculated.

[0064] Table 2 shows the changes of soil pH, salt content, and available phosphorus content, as well as the corn grain yield and phosphorus fertilizer agronomic utilization rate under different treatments. It can be seen that, whether in moderate or severe saline-alkali land, the addition of activator can significantly reduce the soil pH and increase the available phosphorus content, such as in the moderate saline-alkali land MS

[0065]

[0066] Table 2 shows the changes of soil pH, salt content, and available phosphorus content, as well as the corn grain yield and phosphorus fertilizer agronomic utilization rate under different treatments. It can be seen that, whether in moderate or severe saline-alkali land, the addition of activator can significantly reduce the soil pH and increase the available phosphorus content, such as in the moderate saline-alkali land MS30 The average available phosphorus content of corn growth period of MS 10 The average available phosphorus content of corn growth period of MS 50 The average available phosphorus content of corn growth period of MS 10 The average available phosphorus content of corn growth period of MS 30 The average available phosphorus content of corn growth period of MS 10 The average available phosphorus content of corn growth period of MS 30 The average available phosphorus content of corn growth period of MS 50 The average available phosphorus content of corn growth period of MS 10 The average available phosphorus content of corn growth period of MS 30 The average available phosphorus content of corn growth period of MS 50 The average available phosphorus content of corn growth period of MS 30 The average available phosphorus content of corn growth period of MS 50 The average available phosphorus content of corn growth period of MS 30 The average available phosphorus content of corn growth period of MS 50 The average available phosphorus content of corn growth period of MS

[0067] In summary, by using the synergistic effect of low molecular weight organic acid chemical activation, functional microbial inoculant biological stimulation, and capacity reduction, soil improvement, and obstacle elimination and activation, the single effect of single low molecular weight organic acid is broken through. The salt-tolerant and high-efficiency active phosphorus functional microbial inoculant (mixed microbial inoculant is Bacillus megaterium, Aspergillus niger, and Penicillium oxalicum) is used to achieve "relay race" biological activation on the basis of organic acid activation, greatly improving the activation efficiency and effective period. At the same time, modified diatomite with loose pores is used as a substrate carrier to improve the survival rate and active phosphorus efficiency of the microbial inoculant. Loosening the soil breaks the hardening to promote salt leaching, quickly reduces the salt-alkali obstacle, and improves the activity of soil phosphorus solubilizing microorganisms (such as alkaline phosphatase), thereby improving the combined force of multiple synergistic active phosphorus synergies. These effects cannot be achieved by existing technologies and products, and compared with them, there are significant improvements in phosphorus activation effect, efficiency, efficacy, and activation effective period.

Claims

1. A phosphorus-activated slow-release granule formulation for saline-alkali land, characterized in that, The structure comprises a multi-layered spherical coating consisting of a core material, an inner membrane, a wall material, and an outer membrane, arranged sequentially from the inside out. The core material is composed of modified diatomaceous earth, fulvic acid, maltose, ammonium sulfate, and a mixed microbial agent. The inner membrane is composed of a mixed starch, polyvinyl alcohol (PVA), and a plasticizer. The wall material is composed of citric acid and oxalic acid. The outer membrane is composed of vegetable oil and resin. The mass ratio of each component in the core material is: 20-40 parts modified diatomaceous earth, 3-6 parts fulvic acid, 2-5 parts maltose, 1-2 parts ammonium sulfate, and 1-2 parts mixed microbial agent. The modified diatomaceous earth is natural diatomaceous earth with a SiO2 content ≥70 wt.% and a particle size of 0.05-0.1 mm, calcined at 400-450 ℃ for 1-2 hours, or modified in sulfuric acid at 35-40 ℃ and a concentration of 1.5-2 mol / L for 35-45 minutes. The modified diatomaceous earth has a specific surface area ≥ 100 m². 3 / g, porosity ≥80%; the fulvic acid is an effective content ≥90% on a dry basis, amino acid content ≥10%, 10% aqueous solution pH 4.0~6.0, heavy metal content <20 ppm, and powder passing through 100 mesh; the maltose is a mixture of α-maltose and β-maltose in any ratio, with an effective content ≥95% on a dry basis, solubility ≥62 g / 100 g water, and powder passing through 80~100 mesh; the ammonium sulfate is an effective content ≥98% on a dry basis, solubility ≥70 g / 100 g water at room temperature, and powder passing through 80~100 mesh; the mixed bacterial agent is Bacillus megaterium (… Bacillus megaterium ), Aspergillus niger ( Aspergillus niger ), Penicillium oxalate ( Penicillium oxalicum The following are the components of the inner coating:

1. Mixed in a 1:1:1 weight ratio, the microbial agent is a powder passed through a 100-mesh sieve; 2-4 parts by weight of mixed starch, 1.5-3 parts by weight of polyvinyl alcohol, and 1-2 parts by weight of plasticizer; the mixed starch is a 7:3 weight ratio of corn starch and potato starch, passed through a 120-mesh sieve; the polyvinyl alcohol has an effective ingredient content ≥99% on a dry basis, a viscosity ≥30, and is a powder passed through a 100-mesh sieve; the plasticizer is a viscous liquid with an effective ingredient content ≥95%; 3. 30-50 parts by weight of citric acid and 40-60 parts by weight of oxalic acid; the citric acid has an effective ingredient content ≥99% on a dry basis, a moisture content <0.5%, a heavy metal content <5 ppm, and a pH of 2-3 for a 1% solution. The powder; the oxalic acid powder has an effective ingredient content of ≥99% on a dry basis and a moisture content of <0.3%; the outer coating has the following mass ratio: 3-6 parts vegetable oil and 1-2 parts resin; the vegetable oil is at least one of castor oil, soybean oil, peanut oil, olive oil, tung oil, rapeseed oil, and cottonseed oil; the resin is at least one of polyethylene resin, polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride, polyvinyl alcohol resin, polypropylene resin, rosin resin, polyurethane resin, and polyethylene glycol resin; the materials and thicknesses of the outer and inner coatings are configured such that, under the action of soil moisture, the outer coating preferentially dissolves to release citric acid and oxalic acid in the wall material, rapidly reducing the pH of the rhizosphere soil; after the organic acid concentration decreases, the inner coating gradually dissolves to release the mixed bacterial agent in the core material, realizing a sequential relay of chemical activation and microbial activation.

2. The phosphorus-activated slow-release granules for saline-alkali land according to claim 1, characterized in that, 20 parts modified diatomaceous earth, 5 parts humic acid, 3 parts maltose, 1 part ammonium sulfate, and 1 part mixed bacterial agent are mixed evenly. The mixed bacterial agent is *Bacillus megaterium* (…). Bacillus megaterium ), Aspergillus niger ( Aspergillus niger ), Penicillium oxalate ( Penicillium oxalicum Mix the starch and polyvinyl alcohol in a 1:1:1 weight ratio, add water (13.1% of total weight) and stir thoroughly. Granulate the mixture into particles with a diameter of 0.3-0.7 mm. Mix 3 parts starch and 2 parts polyvinyl alcohol, add distilled water in a 1:5 weight ratio, place in a 90 ℃ water bath, stir for 40 min, add 1.5 parts glycerol and stir for another 40 min. Cool to room temperature to prepare an inner coating material. Coat the inner coating material evenly onto the surface of the particles. Mix 40 parts citric acid and 50 parts oxalic acid with the coated particles and further granulate by roller granulation into particles with a diameter of 0.5-1.0 mm.

3. The method for preparing the phosphorus-activated sustained-release granules for saline-alkali land according to claim 1, characterized in that, The steps are as follows: Step 1: Mix modified diatomite, fulvic acid, maltose, ammonium sulfate and mixed bacterial agents according to mass parts, add 10-15 wt.% of water based on the total weight, stir well, and granulate into core particles with a diameter of 0.5-1 mm; Step 2: Mix mixed starch and polyvinyl alcohol according to mass parts, add distilled water according to a weight ratio of 1:(4-5), place it in a water bath at 90 °C, stir for 35-40 min, then add glycerol and continue to stir for 40-45 min, and cool to room temperature to prepare an inner coating material; Step 3: Uniformly coat and wrap the inner coating material on the core particles, with an inner coating thickness of 0.05-0.1 mm; Step 4: Mix citric acid and oxalic acid according to mass parts, add the core particles coated with the inner coating prepared in Step 2, and granulate by drum granulation into particles with a diameter of 0.6-1.1 mm; Step 5: Add vegetable oil to the reaction tank, stir well, add the corresponding mass parts of resin, inject nitrogen into the reaction tank for 10 min and discharge air, heat the reaction tank, raise the temperature for 5 hours, set the reaction temperature at 120-150 °C, keep warm for 5 hours and then cool to 40-80 °C to prepare an outer coating material; Step 6: Use spray condensation granulation to spray the outer coating material on the surface of the particles, and the condensation spray conditions are that the outer coating feeding temperature is 60-80 °C, the condensation temperature is 0-5 °C, and the outer coating thickness is 0.02-0.04 mm.

4. Application of the sustained-release granule agent according to any one of claims 1-2 in activating phosphorus in saline-alkali soil.

5. The application according to claim 4, characterized in that: The application rate and frequency vary depending on the degree of soil salinity. For slightly saline-alkali soil with a total salt content < 3 g / kg or 7.5 < pH < 8.5, the application rate for strip application is 10-20 kg per mu, and the application rate for hole application is 10-15 kg per mu, with an application frequency of once every 4-5 years; for moderately saline-alkali soil with a total salt content of 3-6 g / kg or a pH value of 8.5-9.5, the application rate for strip application is 20-40 kg per mu, and the application rate for hole application is 15-30 kg per mu, with an application frequency of once every 3-4 years; for severely saline-alkali soil with a total salt content > 6 g / kg or pH > 9.5, the application rate for strip application is 40-60 kg per mu, and the application rate for hole application is 30-40 kg per mu, with an application frequency of once every 2-3 years.

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